Without limiting the scope of the present disclosure, this background is described in connection with external fixation devices. Generally, external fixation devices are commonly used on both the upper and lower limbs for both adults and children in a variety of surgical procedures including limb lengthening, deformity correction and treatment of fractures, mal-unions, non-unions and bone defects. Such orthopedic fixation systems may be utilized to treat fractures of the skeleton, soft tissue injuries, delayed union of the skeleton when bones are slow to heal, nonunion of the skeleton when bones have not healed, mal-union where broken or fractured bones have healed in a mal-position, congenital deformities where bones develop a mal-position, and bone lengthening, widening, or twisting. These systems are sometimes called “halo” systems or “hexapod” type circular ring fixation systems.
Such ring-based fixator systems are typically placed on the affected patient by medical personnel in such a way as to align the affected body part during the healing process, holding the affected body part in the proper position for treatment. For example, such fixators may be used to stabilize bone fragments by holding the fragments in a relatively fixed spatial relation, and are adjustable orthopedic systems that allow the physician or other medical professional to reorient one fragment with respect to another along all six axes in an acute motion, usually by loosening one or more clamps and effecting the corrective motion manually and then retightening clamps to stably hold the fragments in the desired position. Since applications of such devices can include a wide variety of deformities, body sites, and surgical implementations, there is a need for fixation devices that can initially be acutely adjusted in order to accommodate such variabilities, and subsequently maintain the affected body part in one desirable position. Moreover, a typical treatment regimen requires frequent adjustments to be performed by the patient and/or during repeated visits to medical professionals so that the fixation device can be periodically and gradually adjusted, providing the desired orientation to the affected body part and setting the proper amount of support and stretching or compression for healing.
One common external fixation device of type discussed above is known as the Ilizarov apparatus. The Ilizarov external fixation procedure involves a rigid framework consisting of several rings or arches that are placed externally around the limb, and attached to injured (e.g., due to fracture) or surgically separated (e.g., for limb lengthening and deformity correction) bone segments using special bone fasteners (wires and pins) inserted into the bone segment and connected to the related section of the external rigid framework.
Another common external fixation device of the type discussed above is a Taylor Spatial Frame, as described in U.S. Pat. Nos. 6,030,386, 5,891,143, and 5,776,132. The Taylor Spatial Frame is a hexapod-type of device and shares many components and features of the Ilizarov apparatus. The Taylor Spatial Frame consists of two external fixator rings attached to bone segments by wires or half-pins, and connected together by six struts that may be lengthened or shortened as necessary. Adjustment of strut lengths allows manipulation of the bone segments in 6 axes (e.g., lengthening/shortening, external/internal rotation, anterior/posterior horizontal translation, medial/lateral horizontal translation, anterior/posterior angular translation, and medial/lateral angular translation) to correct linear, angular and rotational deformities simultaneously.
Looking specifically into their functionality, with most fixators based on rings or arches like those discussed above, the opposite rings/frames of the rigid framework are connected by either threaded or telescopic connection rods or by assembled uni-planar or multi-planar angular hinges, which allow the medical professional to adjust the relative position of the rings to each other longitudinally or angularly over a period of time. This allows new bone to gradually form in the gap between bone segments created by this distraction technique. Once the desired position of bone segments is achieved over the course of time (e.g., 2-6 weeks), the external apparatus is stabilized into a fixed position and left on the bone segments until the fracture is healed or newly formed bone is completely or substantially mineralized, which could take up to an additional 3-6 months, depending on the nature of pathology and degree of deformity.
Based on the above, current orthopedic fixation systems may have a number of mechanical benefits, including flexibility in positioning one ring with respect to another, and strength during compressive loading. However, configurations that can provide a full six degrees of freedom between two circular fixator rings typically require adding struts to increase range of movement, which is problematic from a clinical use perspective, or require having fewer struts, which requires multiple degrees of controllable motion within each strut and thereby unfortunately reducing the overall system strength in supporting loads. Accordingly, an orthopedic ring fixation system is needed that provides six degrees of freedom, but that is easy to configure and does not reduce the overall system strength. Still other objects and advantages of the invention will become clear upon review of the following detailed description in conjunction with the appended drawings.